Naphthyl organic compounds

ABSTRACT

A liquid crystalline compounds:  
     R 1 —A—(X) m —(B) n —R 2    
     are described where A is naphthyl, fluorinated naphthyl or brorninated naphthyl; B is phenyl, methylated phenyl, brominated phenyl, fluorinated phenyl or pyrimidine; R 1  and R 2  are independently C 1-15  alkyl, alkoxy, alkynyl, thioalkyl, perfluoroalkyl, perfluoroalkoxy or Br, CN, SCN, NCS and hydrogen; X is COO or C═C, m is 0 or 1, and n is 1.

[0001] This invention relates to compounds containing a naphthyl groupand which have liquid crystalline properties and/or which are suitablefor use as constituents of liquid crystal materials. The invention alsorelates to use of such compounds in liquid crystal materials.

[0002] Liquid crystal materials and devices exploit the electro-opticalpropertiesof nematic and cholesteric (N or N*), or smectic (S) withparticularly useful smectic phases being chiral smectic C (S_(c)*) orsmectic A.

[0003] Liquid crystal materials which show ferroelectric S_(c)* phaseare useful in fast switching displays such as television or VDU screensas the S_(c)* phase can be swithched in a few milliseconds or evenmicroseconds. The principle of S_(c)* switching is described inter aliaby N A Clark and S T Lagerwall in App Phys Lett 36 (1980) p899.

[0004] Materials which show an S_(A) liquid crystal phase may be used indisplay devices which exploit the electroclinic effect.

[0005] The use of liquid crystal materials to exhibit electro-opticaleffects in displays and other optical devices such as digitalcalculators. watches, meters and alphanumeric laptop computers is nowwell known. However, known liquid crystal materials are not ideal in allrespects and a considerable amount of work is currently being carriedout in the art to improve their properties.

[0006] Liquid crystal materials normally consist of specially selectedmixture compositions and improved materials are often obtained byforming new mixtures having an improved combination of properties.

[0007] The composition of a liquid crystal mixture is generally selectedso that the mixture shows desirable properties. In particular suchproperties include:

[0008] (1) a liquid crystalline temperature range—including roomtemperature (20° C.)—which is as wide as possible;

[0009] (2) a melting point (solid-to-liquid crystal transitiontemperature) which is as low as possible;

[0010] (3) a clearing point (liquid crystalline to isotropic liquidtransition temperature) which is as high as possible;

[0011] (4) a positive or negative (as appropriate) dielectric anisotropy(permittivity measured parallel to the molecular axis less that measuredperpendicular to the molecular axis) which is as great as possible inorder to minimise the display voltage;

[0012] (5) a viscosity which is as low as possible in order to minimisethe display switching speeds;

[0013] (6) an electro-optical response which varies as little aspossible with temperatures;

[0014] (7) a good chemical and photochemical stability;

[0015] Examples of further particular properties useful in specificapplications include:

[0016] (8) a good multiplexability;

[0017] (9) an ability to switch dielectric anisotropy with frequency;

[0018] (10) a birefringence of selected magnitude;

[0019] (11) specific elastic constants which can be tailored to meetspecific device requirements; and

[0020] (12) high electrical resistivity for certain applications.

[0021] Liquid crystal materials and devices exploit the electro-opticalproperties of nematic or cholesteric (N and N* respectively), or smectic(S) in particular chiral smectic C (S_(c)*) or smectic A (S_(a)) phase.The most common type of liquid crystal materials in use are those whichshow a nematic phase and these are extensively used in, for example,watches, clocks, calculators, electronic displays etc.

[0022] For some applications of liquid crystal materials a highbirefringence is sought, eg in so called “electrically controlledbirefringence” (ECB) effect devices (see, for example, M F Schieckel andK Fahrensohn Applied Physics Letters 19 p2912 1971), in thin filmtransistors and supertwisted nematic devices. It is rare for therequisite desirable properties to be found in a single liquidcrystalline compound and generally liquid crystalline materials consistof mixtures of component compounds. Very many liquid crystallinecompounds suitable for such uses are known and will be apparent to thosein the art.

[0023] Some liquid crystalline compounds based on the phenyl-naphthalenesystem are known eg

[0024] For example, Bull Soc Chim Fr 11-12(2) p2521-2426 (1975)describes compounds where A is alkoxy and B is alkyl or alkoxy, and HelvChim Acta 68(5) p1406-1426 describes those in which a is alkyl or alkoxyand B is cyano or trifluoromethyl.

[0025] It is the aim of this invention to provide novel compounds whichprovide improved or alternative liquid crystalline and/or monotropiccharacteristics.

[0026] According to this invention, liquid crystal naphthyl compounds offormula I are provided;

R₁—A—(X)_(m)—(B)_(n)R₂  Formula I

[0027] where A is selected from nathyl, fluorinated naphthyl, brominatednaphthyl, B is selected from phenyl, methylated phenyl, brominatedphenyl, fluorinated phenyl, thiophene, pyrimidine and pyridine, R₁ andR₂ are independently selected from alkyl, alkoxy, alkynyl, thioalkyl,Br, CN, SCN, NCS, perfluoroalkyl, perfluoroalkoxy and hydrogen, X isselected from C≡C, COO and C═C, m is 0 or 1, n is 0 or 1 where m is 1and n is 0 where m is 0;

[0028] provided that

[0029] where A is naphthyl, n is 1and m is 0 then B is selected frommethylated phenyl, brominated phenyl, thiophene, pyrimidne and pyridine;

[0030] and further provided that

[0031] where A is naphthyl, X is C≡C, m is 1 and n is 1, then B isselected from thiophene, pyrimidine and pyridine.

[0032] The preferred embodiments of the invention discussed below areinter alia chosen with respect to their liquid crystalline properties.particularly with respect to suitability for use in high birefringencenematic or ferro-electric Sc* liquid crystal materials. Preferably foruse in nematic materials alkyl, alkoxyl, thioalkyl and alkynylsubstituents R₁ and R₂ contain 1-15 carbon atoms, and more preferablycontain 1-5 carbon atoms for use as nematic materials and 3-9 carbonatoms for use as smectic materials. Preferably for smectic C materialsR₁ and R₂ are selected from n-alkyl or n-alkoxy.

[0033] According to a further aspect of this invention compoundssuitable for inclusion in devices utilising pretransitionalcharacterisitcs of liquid crystalline materials in the isotropic phaseare provided, of general Formula II

R₃—J—(Y)_(p)—(Z)_(q)—R₄  Formula II

[0034] where J is selected from nathyl, fluorinated naphthyl, brominatednaphthyl, Z is selected from phenyl. methylated phenyl, brominatedphenyl, fluorinated phenyl, thiophene, pyrimidine and pyridine, R₁ andR₂ are independently selected from alkyl, alkoxy, alkynyl. thioalkyl,Br, CN, SCN, NCS, perfluoroalkyl, perfluoroalkoxy and hydrogen, Y isselected from C═C, COO and C≡C, p is 0 or 1, q is 0 or 1 where p is 1and q is 0 where p is 0;

[0035] Typically such compounds can be utilised in devices such asOptical Kerr Effect devices. Such devices are often used as opticalshutters or optical modulators, and rely on the the fact thatbirefringence (Δn) of a medium being proportional to the square of anapplied electric field. Such an effect is often termed the quadraticelectro-optic effect and can be investigated using degenerate four wavemixing (P Madden et al IEEE J of Quantum Electronics QE22 No 8 August1986 p1287).

[0036] Preferably where R₃ and R₄ are selected from C₁₋₁₅ alkyl, alkoxy,thioalkyl and alkynyl; more preferably C₁₋₉ and even more preferablyC₃₋₉.

[0037] Preferred overall structures of formula I and formula II are nowlisted:

[0038] Naphthyl materials of formula I and formula II may be generallyprepared by various routes which will be apparent to those in the art.Typical routes which can be used include reaction of an appropriatephenyl (or equivalent eg thiophene, pyrimidine etc) boronic acid with anappropriate naphthol triflate. Alternatively, an appropriate boronicacid can be reacted with such appropriate compounds as bromonitro-egacid can be reacted with such appropriate compounds as bromonitro-egappropriate benzene, thiophene residues etc, for CN and NCS terminalgroups. Terminal groups of alkyls, alkoxys, alkynyls and thioalkyls canbe achieved by well known alkylation, 0-alkylation, alkynylation (viaappropriate triflate) and thioalkylation routes respectively. Naphthylmaterials of where m and n are 0 can be prepared from bromonaphthol byusing eg alkylation, thioalkylation etc, and also be followed by egcyanation (by use of eg CuCN) etc.

[0039] The invention also provides a liquid crystal material being amixture of at least two compounds. at least one of which is a naphthylcompound of formula I. This material may show a nematic or smectic (e.g.S_(a), S_(c)* or S_(c)) charateristics and also sometimes isotropicproperties.

[0040] In particular many naphthyl compounds of formula I have a highanisotropy in polarisability (Δa), making them suitable for applicationsin which this characteristic is required, as discussed above. Naphthylcompounds of formula I may be used as components of nematic liquidcrystal materials together with other liquid crystalline compounds. forexample compounds of general formula III:

[0041] where R₁ is selected from a group comprising hydrogen, alkyl,alkoxy, alkynyl, thioalkyl, CN, and Br; R₂ is selected from a groupcomprising hydrogen, NCS, SCN, CN, alkyl, alkoxy, alkynyl, andthioalkyl; m and n are 1 or 0 such that m is 1 where n is 0 and m is 0where n is 1 or 0; p is independently 1 or 0; X is selected from a groupcomprising of naphthyl, fluorinated naphthyl and brominated naphthyl;and Y is selected from a group comprising of phenyl, methylated phenyl,brominated phenyl, thiophene and pyrimidine and pyridine.

[0042] The mixture may also contain such materials as phenyl thiazolenesof typical structure such as that seen in Formula IV

[0043] where typically R₃ is CN, alkyl, alkoxy etc.

[0044] Other suitable mixture materials include for example those ofmaterials described in application Ser. No. 892828.6, where their use aspolymer network materials suitable for eg dispersion within a matrix oftransparent polymer is described.

[0045] The mixture may also contain one or more fluorinatedcyanobiphenyls or terphenyls of formula V:

[0046] where R₁ is C₁₋₁₀ n-alkyl or n-alkoxyl and thefluorosubstituent(s) may be in any one or two of the availablesubstitution positions. Compounds of the formula V are known (PCT/GB89/00647) and with their inclusion in mixture, it is possible to furtherincrease birefringence.

[0047] A nematic liquid crystal of this invention may also contain oneor more optically active compounds to induce a cholestric phase and oneor more pleochroic dyes.

[0048] The materials of this aspect of the invention may be used in anyof the known forms of liquid crystal display devices, for example atwisted nematic device, Freedricks effect device, cholesteric memorymode device, cholesteric to nematic phase change effect device, dynamicscattering effect device, two frequency switching effect device, asupertwist effect device, or a thermometer using a thermochromicmaterial. The method of construction and operation of such devices, andcharacteristics of a liquid crystal material suitable for use therein,are well known in the field. Typically an electro-optical display devicewill consist of 2 substrates between which a layer of the liquid crystalmaterial may be sandwiched. At least one of the substrates is opticallytransparent and both have addressable electrodes which are preferablymade of a transparent material on their opposing faces. By applying anelectric field across the layer of liquid crystal material via theelectrodes an electro-optical effect is achieved which may be vieweddirectly or preferably through one or more polarising filters.

[0049] Another aspect of the invention is a material, being a mixture ofcompounds, characterised in that the mixture is suitable for inclusionin devices utilising pretransitional characterisitcs of liquidcrystalline mixtures in the isotropic phase and that the mixtureincludes at least one compound of formula II. Such materials alsocontain compound(s) of formula III and/or compound(s) of formula IVand/or compound(s) of formula V.

[0050] Compounds of formula II and also materials including compound(s)of formula II may be used in devices that utilise the optical KerrEffect. Typically optical Kerr effect devices comprise a glass cellcontaining two electrodes, where the glass cell is filled with a polarliquid. The device is frequently termed a Kerr cell. The Kerr cell canbe positioned between two crossed polarisers having transmisssion axesat ±45° to an electric field applied across the Kerr cell. With zerovoltage applied across the Kerr cell no light will be transmitted andthe cell operates as a closed shutter. Application of a modulatingvoltage generates a field causing the Kerr cell to function as avariable wave plate and thus operating the Kerr cell as a shuttercapable of opening proportionately to the applied field.

[0051] Nematic materials of this invention may be particularly suitablefor use in ECB effect devices, due to the high birefringence of thematerials. They may also be particularly suitable for use in polymerdispersed liquid crystal (PDLC) materials in which small droplets of aliquid crystal material are dispersed within a matrix of a transparentpolymer.

[0052] Non-limiting examples illustrating this invention will now bedescribed with reference to the accompanying figures, of which FIGS. 1to 5 schematically show synthetic routes for exemplified compounds 1 to5, and FIGS. 6 and 7 are schematic representations of a liquid crystaldevice of the invention and a Kerr cell of the invention.

EXAMPLE 1 Preparation of

[0053]

[0054] With reference to FIG. 1 it can be seen that

[0055] Step 1.1 5-Bromo-hydroxpyrimidine

[0056] Bromine (67.00 g, 0.419 mol) is added slowly dropwise to astirred solution of 2-hydroxypyrimidine hydrochloride (50.00 g, 0.377mol) in water (200 ml) at room temperature (exothermic reaction but nocooling used). The solution is stirred for 1 hour (until cool) and thenwater and excess bromine is removed in vacuo to give a pale yellow solidwhich is dried in vacuo (0.1 mmHg) giving 5-Bromo-2-hydroxypyrimidine asa solid which is still “wet”as a yield of 100 g.

[0057] Step 1.2 5-Bromo-2-chloropyrimidine

[0058] A solution of compound 1.1 (assume 100% yield from previouspreparation; 65.98 g, 0.377 mol) in phosphorous oxychloride (500 ml) andN,N-dimethylaniline (20 ml ) is heated under reflux for 4 hours. thecooled mixture is carefully poured onto ice and extracted into ether(×2). The combined ethereal extracts are washed with aqueous sodiumhydrogen carbonate and dried (MgSO₄). The solvent is removed in vacuo toyield an off-white solid. Yield (based on 2-hydroxypyrimidinehydrochloride) is 23.55 g, 32%.

[0059] Step 1.3 2-Chloro-5-pent-1-ynylpyrimidine

[0060] Quantities: pent-1-yne (3.00 g, 0.044 mol), n-butyllithium (4.40ml, 10.0M in hexane, 0.044 mol), zinc chloride (6.00 g, 0.044 mol),compound 1.2 (8.00 g, 0.041 mol), tetrakis(triphenylphosphine)palladium(O) (1.5 g, 1.30 mol).

[0061] This experimental procedure is a zinc coupling reaction. Then-butyllithium solution is added dropwise to a stirred, cooled (−5° C.to 0° C.) solution of the pent-1-yne in dry THF under dry nitrogen. Thismixture is stirred fro 10 minutes and then a solution of the zincchloride (dry) in dry THF is added dropwise at about −5° C. to 0° C. Themixture is stirred at room temperature for 15 minutes and a solution ofcompound 1.2 in dry THF is added dropwise at −5° C. to 0° C. followed byaddition of the tetrakis (triphenylphosphine)palladium(O). the mixtureis heated under reflux for 22 hours (glc analysis revealing a completereaction). The crude product is purified by column chromatography[silica gel/petroleum fraction (bp40-60° C.)- dichloromethane, 1:20] togive a colourless solid which is crystalised from hexane to yieldcolourless crystals.Yield is 6.27 g (85%).

[0062] Step 1.4 2-butoxy-6-(5-pent-1-ynylpyrimidine-2-yl)naphthalene

[0063] Quantities: compound 1.3 (1.60 g, 8.86 mol),6-butoxynaphth-2-ylboronic acid (2.60 g, 0.011 mol),tetrakis(triphenylphosphine)palladium(O) (0.35 g, 0.30 mol).

[0064] This experimental procedure is a boronic acid coupling reaction.A solution of the boronic acid in dimethoxyethane is added to a stirredmixture of compound 1.3 and tetrakis(triphenylphosphine)palladium(O) indimethoxymethane and 2M sodium carbonate at room temperature under drynitrogen. The mixture is heated under reflux for 18 hours (glc analysisrevealing a complete reaction). The crude product is purified by columnchromatography [silica gel/petroleum fraction (bp40-60°C.)-dichloromethane, 1:2] to give a colourless solid which isrecrystallised from ethyl acetate-ethanol (1:1) to yield colourlesscrystals. Yield is 2.25 g (74%).

Example 2 Preparation of

[0065]

[0066] With reference to FIG. 2 it can be seen that

[0067] Step 2.1 2-pent-1-ynylthiophene

[0068] Quantities: pent-1-yne (6.80 g, 0.10 mol), n-butyllithium (10.0ml, 10.0M in hexane, 0.044 mol), zinc chloride (13.60 g, 0.10 mol),2-bromothiophene (16.00 g, 0.098 mol), tetrakis(triphenylphosphine)palladium(O) (3.40 g 2.94 mol).

[0069] The experimental procedure is as described for step 1.3. Thecrude product is distilled to yield a colourless liquid. Yield is 12.96g (88%).

[0070] Step 2.2 5-pent-1-ynylthiophen-2ylboronic acid

[0071] Quantities: compound 2.1 (10.0 g, 0.067 mol), n-butyllithium(6.80 g. 10.0M in hexane, 0.068 mol), trimethyl borate (14.20 g, 0.137mol).

[0072] This experimental procedure is a standard boronic acidpreparation and yields a brown solid. The yield is 12.00 g (93%).

[0073] Step 2.3 2-(6-Cyanonaphth-2-yl)-5-pent-1-ylthiophene

[0074] Quantities: 6-cyanonaphth-2-yl triflate (2.00 g, 6.64 mol),5-pent-1-ynylthiophen-2-ylboronic acid (1.55 g, 7.99 mmol), tetrakis(triphenyl phosphine)palladium(O) (3.40 g 2.94 mol), lithium chloride(0.85 g, 0.020 mol).

[0075] This experimental procedure is as for the boronic acid couplingreaction described in step 1.4, except for the addition of lithiumchloride as a catalyst. The crude product is purified by columnchromotography [silica gel/petroleum fraction (bp40-60°C.)-dichloromethane, 1:1] to give a yellow solid, which isrecrystallised from ethanol to yield pale yellow crystals. Yield is 1.55g (78%).

Example 3 Preparation of:

[0076]

[0077] With reference to FIG. 3 it can be seen that

[0078] Step 3.1 2-Bromo-6-ethoxynaphthalene

[0079] This experimental procedure is an O-alkylation. A solution ofbromomethane (48.90 g, 0.45 mol) is added dropwise to a stirredrefluxing mixture of 6-Bromo-2-naphthol (40.00 g, 0.18 mol) andpotassium carbonate (63.00 g, 0.46 mol) in acetone. The stirred mixtureis heated under reflux for 24 hours (ie until glc analysis reveals acomplete reaction). The potassium carbonate is filtered off, water isadded to filtrate and the product is recrystallised from ethanol to givea yield of 43.92 g (97%).

[0080] Step 3.2 2-Ethoxy-6-cyanonaphthalene

[0081] This experimental procedure is a cyanation where compound 3.1(3.00 g, 0.012 mol) is reacted with Copper (I) cyanide (1.30 g. 0.015mol), with the crude product purified by column chromatography [silicagel/petroleum fraction (bp40-60° C.)-dichloromethane, 1:2) to give acolourless solid which is distilled [Kugeklrohr, 170° C. (maximum) at0.1 mmHg] to yield 1.75 g (74%) of colourless solid.

[0082] Step 3.3 1-Bromo-6-cyano-2-ethoxynaphthalene

[0083] A solution of bromine (1.72 g, 0.011 mol) in glacial acetic acid(4 ml) is added dropwise to stirred solution of compound 3.2 (1.93 g,9.80 mol) in glacial acetic acid (35 ml) at 80° C.. The solution isstirred for an additional 10 minutes (glc revealing a complete reactionand only one product peak). The solution is added to water and theproduct is extracted from ether (×2) and the combined ethereal extractsare washed with water and sodium metabisulphite and dried. The solventis removed in vacuo and the residue purified by column chromotography[silica gel/petroleum fraction (bp40-60° C.)-dichloromethane, 1:1] togive a colourless solid (1.72 g) which is recrystallised fromhexanedimethoxymethane (1:1) to yield 1.55 g (57%) colourless crystals.

Example 4 Preparation of

[0084]

[0085] With reference to FIG. 4 it can be seen that

[0086] Step 4.1 2-Bromo-6-thiobutylnaphthalene

[0087] Trifluoromethanesulphonic acid (14.85 g, 0.099 mol) is addeddropwise to a stirred mixture of 6-bromo-2-naphthol (20.00 g, 0.090 mol)and butanethiol (8.07 g, 0.090 mol) in dry benzene (180 ml) under drynitrogen. The resulting solution is stirred at 50° C. for 4 hours (glcanalysis revealing a complete reaction), cooled and poured into ice-coldwater. The product is extracted into ether (×2), the combined organicphases washed with 5%sodium hydroxide and water and dried (MgSO₄). Thesolvent can then be removed in vacuo and the residue distilled to give acolourless solid. Yield is 13.80 g (52%).

[0088] Step 4.2 6-Thiobutylnaphth-2-ylboronic acid

[0089] Quantities: compound 4.1 (6.80 g, 0.023 mol), n-butyllithium(2.30 ml. 10.0M in hexane, 0.023 mol), trimethylborate (4.80 g, 0.046mol).

[0090] This experimental procedure is a preparation of the appropriateboronic acid by standard procedures, giving a yield of 3.49 g (58%)after the product of the reaction is extracted into 10% potassiumhydroxide, the basic extract washed with ether and acidified, extractedinto ether and dried (MgSO₄), and removal of solvent in vacuo to give acolourless liquid.

[0091] Step 4.3 2-(4-Cyanophenyl)-6-thiobutylnaphthalene

[0092] Quantities: compound 4.2 (1.81 g, 6.96 mol),4-bromobenzonitrile(1.15 g,6.32 mol), tetrakis(triphenylphosphine)palladium(O) (0.235 g,0.22 mol).

[0093] This experimental procedure is a boronic acid coupling reactionas previously described in step 1.4, followed by purification of thecrude product by column chromatography [silica gel/petroleum fraction(bp40-60° C.)-dichloromethane, 1:1] to give a colourless solid which isthen recrystallised from ethanol-ethyl acetate (4:1) to yield 1.63 g(81%) of colourless crystals.

Example 5 Preparation of

[0094]

[0095] With reference to FIG. 5 it can be seen that

[0096] Step 5.1 2-Bromothiophene

[0097] A solution of thiophene (31.88 g, 0.380 mol) andN-bromosuccinimide (64.00 g, 0.360 mol) in a mixture of chloroform (80ml) and glacial acetic acid (80 ml) was heated under reflux (withstirring) for 0.5 hours (constant glc analysis revealed a completereaction with minimal formation of 2.5-dibromothiophene). The reactionmixture was diluted with water and washed with dichloromethane (2×100ml); the combined organic extracts were washed successively with water(300 ml) and aqueous potassium hydroxide (5%, 300 ml) before being dried(MgSO₄). The solvent was removed in vacuo and the residue was distilledto give a colourless liquid.

[0098] Yield 24.34 g (42%).

[0099] Step 5.2 2-Bromo-5-nitrothiophene

[0100] Nitric acid (24.00 g, 1.42 sp gr, 0.381 mol) in acetic anhydride(50 ml) at 0° C. was added dropwise to a cooled (0° C.) rapidly stirredsolution of the compound of step 5.1 (24.77 g, 0.152 mol) in aceticanhydride (50ml). At the end of the addition the stirring was continuedfor 0.5 hr and the mixture was refrigerated overnight. The mixture waspoured into ice water (400 ml) and the precipitate was filtered off,dissolved in ether (2×200 ml), and washed with water until free of acid.The solvent was removed in vacuo and the residue was purified by columnchromatography [silica gel/petroleum fraction (bp 40-60° C.),dichloromethane, 5:1] and was recrystallised fromethanol/dimethoxyethane, 100:1 to give a pale yellow solid which wasdried in vacuo (P₂O₅) to give 66% yield of 20.89 g.

[0101] Step 5.3 2-(6-Thiobutyl-2-naphthyl)-5-nitrothiophene

[0102] Quantities: Compound of step 4.2 (4.00 g, 0.015 mol), compound ofstep 5.2 (3.31 g, 0.016 mol), tetrakis(triphenylphosphine)palladium(O)(0.910 g, 0.001 mol), sodium carbonate (15.8 ml, 2.0M, 0.03 mol).

[0103] The compound of step 5.2 was added all at once to a rapidlystirred mixture of the palladium catalyst, the compound of step 4.2, andaqueous sodium carbonate solution in dimethoxymethane under drynitrogen. The reaction mixture was refluxed overnight (tlc and glcrevealed a complete reaction) and the product was extracted into ether;the combined ethereal solutions were washed with saturated sodiumchloride solution and dried (MgSO₄). The solvent was removed in vacuoand the product was purified by column chromatography [silicagel/petroleum fraction (bp40-60), dichloromethane, 5:1] to give anorange solid with a 71% yield (3.41 g).

[0104] Step 5,4 2-(6-thiobutyl-2-naphtyl)-5-aminothiophene

[0105] A stirred solution of compound of step 5.3 (2.62 g, 0.008 mol)and palladium on carbon (10%, 2.22 g) in ethanol and tetrahydrofuran wasstirred under hydrogen overnight. The catalyst was removed by filtrationthrough “Hyflo supercel” and the solvent was removed in vacuo to afforda black solid which was used in the next step without purification afteryielding 2.39 g (100%), purity (glc) 50%.

[0106] Step 5.5 2-(6-thioputyl-2-naphthyl)-5-isothionatothiophene

[0107] A solution of compound of step 5.4 (2.30 g, 0.007 mol), inchloroform was added to a stirred, cooled (0-5° C.) solution of calciumcarbonate (1.17 g, 0.012 mol) and thiophosgene (0.97 g, 0.008 mol) inwater and chloroform at 0-5° C.. The mixture was heated at 35° C. for 1h (glc and tlc analysis confirmed a complete reaction) and poured intowater. The organic layer was washed with hydrochloric acid (1%, 100 ml)and dried (MgSO₄). The compound was purified by column chromatography[silica gel/petroleum (bp40-60° C.), dichloromethane, 5:1] and wasrecrystallised to give 0.57 g (22% yield) of a pale green solid whichwas dried in vacuo (CaCO₃). having an indicated (hplc) purity of >99%.

[0108] Liquid crystal transition temperatures between crystalline (K),nematic (N), smectic B (S_(B)) and isotropic (I) are given in Table 1below for compounds of Formula I and Formula II. The table also containsa comparison of anisotropy in polarisability Δa with that of4-cyano-(4′pentyl)-1-phenylcyclohexane (5PCH) and the birefringence (Δn)of the compounds. [ ] denotes a virtual phase transition. TABLE 1 PHASETRANSITION TEMPS COMPOUND. (° C.) Δa Δn

D 146 [N 136.5] I

K 84 [79.5] I 4.88

K 163.5 [N 79.5] I 1.41

K 92 [N 107] I 4.11

0.405

K 100.5 S_(B) 104.5 [N 47] I 0.345

K 108.2 N 118.7 I

4.88

6.21

2.37

4.11

[0109] The n measurements are normalized for 25° C. and were carried outusing an Abbe refractometer and using 3 wt % of the compound to bemeasured in a non-polar eutectic nematic host, typically such as

[0110] where R and R′ are alkyl.

[0111]FIG. 6 a liquid crystal cell comprises a layer 1 of liquid crystalmaterial, where the material is a mixture incorporating compounds offormula I, sandwiched between a glass slide 2 having a conducting layer3 on its surface, eg of indium tin oxide, and a glass slide 4 having atransparent conducting layer 5 on its surface. The slides 2,4 bearingthe layers 3,5 are respectively coated with films 6,7 of a polyimidelayer. Prior to construction of the cell the films 6 and 7 are rubbedwith a soft tissue in a given direction, the rubbing directions beingarranged parallel to the construction of the cell. A spacer 8 eg ofpolymethylmethacrylate, separates the slides 2,4 to the requireddistance eg 5 microns. The liquid crystal material 1 is introducedbetween the slides 2,4 by filling the space between the slides 2,4 andspacer 8 and sealing the spacer 8 in a vacuum in a known way.

[0112] A polarizer 9 is arranged with its polarization axis parallel tothe rubbing direction on the films 6,7 and an analyzer (crossedpolariser) 10 is arranged with its polarization axis perpendicular tothat rubbing direction. When a voltage is applied across the cell bymaking contact with the layers 3 and 5 the cell is switched.

[0113] In an alternative device (not shown) based on a cell constructionas shown in FIG. 6 the layers 3 and 5 may be selectively etched in aknown way, eg by photoetching or deposition through a mask, eg toprovide one or more display symbols, eg letters, numerals, words orgraphics and the like as conventionally seen on displays. The electrodeportions thereby may be addressed in a variety of ways which includemultiplexed operation.

[0114]FIG. 7 shows a Kerr cell 20. It comprises a glass cell 21 havingtwo electrodes 22 and 23, which can be filled with a polar isotropicmedium such as compounds of formula II or materials comprising mixturesincluding at least one compound of formula II. The cell 20 can bepositioned between crossed linear polarisers 24 and 25, whosetransmission axes are arranged to be at ±45° to an applied electricfield. Where there is zero voltage across the electrodes 22 and 23, andthe cell 20 acts as a closed shutter. The application of a modulatingelectric field from voltage source 26 generates an electric fieldcausing the cell 20 to act as a variable wave plate and thus operatingas a variable aperture shutter where opening is proportional to theelectric field.

1. A liquid crystalline compound characterised by formula I areprovided; R₁—A—(X)_(m)—(B)_(n)—R₂  Formula Iwhere A is selected fromnathyl, fluorinated naphthyl, brominated naphthyl. B is selected fromphenyl, methylated phenyl, brominated phenyl, fluorinated phenyl,thiophene, pyrimidine and pyridine, R₁ and R₂ are independently selectedfrom alkyl, alkoxy, alkynyl, thioalkyl, Br, CN, SCN, NCS,perfluoroalkyl, perfluoroalkoxy and hydrogen, X is selected from C≡C,COO and C═C, m is 0 or 1, n is 0 or 1 where m is 1 and n is 0 where m is0; provided that where A is naphthyl, n is 1 and m is 0 then B isselected from methylated phenyl, brominated phenyl, thiophene, pyrimidneand pyridine; and further provided that where A is naphthyl, X is C≡C, mis 1 and n is 1, then B is selected from thiophene, pyrimidine andpyridine.
 2. A compound according to claim 1 where at least one ofterminal groups R₁ and R₂ is selected from alkyl, alkoxy, alkynyl andthioalkyl.
 3. A compound according to claim 2 where at least one of thetermianl groups is straight chain.
 4. A compound according to claim 1where B is thiophene and A is naphthyl.
 5. A compound according to claim4 where m is 1 and X is C≡C.
 6. A compound according to claim 5 where atleast one of the terminal groups is alkynyl.
 7. A compound according toclaim 5 where at least one of the terminal groups is NCS.
 8. A compoundaccording to claim 5 where at least one of the terminal groups isthioalkyl.
 9. A compound according to claim 5 where at least one of theterminal groups is CN.
 10. A compound according to claim 6 where one ofthe terminal groups is NCS and the other is alkynyl.
 11. A compoundaccording to claim 4 where m is
 0. 12. A compound according to claim 11where at least one of the terminal groups is alkynyl.
 13. A compoundaccording to claim 11 where at least one of the terminal groups is NCS.14. A compound according to claim 11 where at least one of the terminalgroups is CN.
 15. A compound according to claim 11 where at least one ofthe terminal groups is thioalkyl.
 16. A compound according to claim 1where B is pyrimidyl and A is naphtlhyl.
 17. A compound according toclaim 16 where m is 1 and X is C≡C.
 18. A compound according to claim 17where at least one of the terminal groups is NCS.
 19. A compoundaccording to claim 16 where m is
 0. 20. A compound according to claim 19where at least on of the terminal groups is alkynyl.
 21. A compoundaccording to claim 1 where A is naphthyl, B is phenyl, m is 1, X is C═Cand at least one of the terminal groups is NCS.
 22. A compound accordingto claim 21 where R₂ is NCS and R₁ is alkoxy.
 23. A liquid crystallinematerial, being a mixture of compounds, and characterised in that itcomprises at least one compound according to claim
 1. 24. A liquidcrysatlline material, being a mixture of compounds, and characterised inthat it comprises at least on compound of claims 1 to
 22. 25. A materialaccording to claim 23 and further characterised in that it comprises atleast on compound of formula III

here R₁ is selected from a group comprising hydrogen, alkyl, alkoxy,alkynyl, thioalkyl, CN, and Br; R₂ is selected from a group comprisinghydrogen, NCS, SCN, CN, alkyl, alkoxy, alkynyl, and thioalkyl; m and nare 1 or 0 such that m is 1 where n is 0 and m is 0 where n is 1 or 0; pis independently 1 or 0; X is selected from a group comprising ofnaphthyl, fluorinated naphthyl and brominated naphthyl; and Y isselected from a group comprising of phenyl, methylated phenyl,brominated phenyl, thiophene and pyrimidine and pyridine.
 26. A materialaccording to claim 23 and further characterised in that it comprises atleast one compound of formula IV

where R_(A) is selected from CN, alkyl and alkoxy.
 27. A materialaccording to claim 23 and further characterised in that it comprisess atleast one compound of formula V

where R₁ is C₁₋₁₀ n-alkyl or n-alkoxyl and the fluorosubstituent(s) maybe in any one or two of the available substitution positions.
 28. Aliquid crystal device characterised in that it uses a material accordingto claim
 23. 29. A liquid crystal device characterised in that itcomprises a material according to claim
 24. 30. A liquid crystalcompound characterised in that it is suitable for inclusion in devicesutilising pretransitional characterisitcs of liquid crystallinematerials in the isotropic phase and is given by formula IIR₃—J—(Y)_(p)—(Z)_(q)—R₄  Formula II where J is selected from nathyl,fluorinated naphthyl, brominated naphthyl, Z is selected from phenyl,methylated phenyl, brominated phenyl, fluorinated phenyl, thiophene,pyrimidine and pyridine, R₁ and R₂ are independently selected fromalkyl, alkoxy, alkynyl, thioalkyl, Br, CN, SCN, NCS, perfluoroalkyl,perfluoroalkoxy and hydrogen, Y is selected from C≡C, COO and C═C, p is0 or 1, q is 0 or 1 where p is 1 and q is 0 where p is 0;
 31. A compoundaccording to claim 30 where at least one of terminal groups R₃ and R₄ isselected from alkyl, alkoxy, alkynyl and thioalkyl.
 32. A compoundaccording to claim 31 where at least one of the termianl groups isstraight chain.
 33. A compound according to claim 30 where Z isthiophene and J is naphthyl.
 34. A compound according to claim 33 wherep is 1 and X is C≡C.
 35. A compound according to claim 34 where at leastone of the terminal groups is alkynyl.
 36. A compound according to claim34 where at least one of the terminal groups is NCS.
 37. A compoundaccording to claim 34 where at least one of the terminal groups isthioalkyl.
 38. A compound according to claim 34 where at least one ofthe terminal groups is CN.
 39. A compound according to claim 35 whereone of the terminal groups is NCS and the other is alkynyl.
 40. Acompound according to claim 33 where p is
 0. 41. A compound according toclaim 40 where at least one of the terminal groups is alkynyl.
 42. Acompound according to claim 40 where at least one of the terminal groupsis NCS.
 43. A compound according to claim 40 where at least one of theterminal groups is CN.
 44. A compound according to claim 40 where atleast one of the terminal groups is thioalkyl.
 45. A compound accordingto claim 30 where Y is pyrimidyl and A is naphthyl.
 46. A compoundaccording to claim 45 where p is 1 and X is C≡C.
 47. A compoundaccording to claim 46 where at least one of the terminal groups is NCS.48. A compound according to claim 45 where p is
 0. 49. A compoundaccording to claim 48 where at least on of the terminal groups isalkynyl.
 50. A compound according to claim 30 where J is naphthyl and Yis phenyl.
 51. A compound according to claim 50 where p is 1 and X isC═C.
 52. A compound according to claim 51 where one of the terminalgroups is NCS.
 53. A compound according to claim 50 having a formula


54. A compound according to claim 52 having a formula


55. A compound according to claim 53 having a formula


56. A compound according to claim 54 having a formula


57. A compound according to claim 50 where at least one of the terminalgroups is CN.
 58. A liquid crystalline material, being a mixture ofcompounds, and characterised in that it comprises at least one compoundaccording to claim
 29. 59. A liquid crysatlline material, being amixture of compounds, and characterised in that it comprises at least oncompound of claims 29 to
 57. 60. A material according to claim 58 andfurther characterised in that it comprises at least on compound offormula III

here R₁ is selected from a group comprising hydrogen, alkyl, alkoxy,alkynyl, thioalkyl, CN, and Br; R₂ is selected from a group comprisinghydrogen, NCS, SCN, CN, alkyl, alkoxy, alkynyl, and thioalkyl; m and nare 1 or 0 such that m is 1 where n is 0 and m is 0 where n is 1 or 0; pis independently 1 or 0; X is selected from a group comprising ofnaphthyl, fluorinated naphthyl and brominated naphthyl; and Y isselected from a group comprising of phenyl, methylated phenyl,brominated phenyl, thiophene and pyrimidine and pyridine.
 59. A materialaccording to claim 58 and further characterised in that it comprises atleast one compound of formula IV

where R_(A) is selected from CN, alkyl and alkoxy.
 60. A materialaccording to claim 58 and further characterised in that it comprisess atleast one compound of formula V

where R₁ is C₁₋₁₀ n-alkyl or n-alxoxyl and the fluorosubstituent(s) maybe in any one or two of the available substitution positions.
 63. Aliquid crystal device characterised in that it uses a material accordingto claim 58.